Properties of CaSO4: Mn Phosphor under Vacuum Ultraviolet Excitation

Abstract

The properties of a manganese-activated CaS${\mathrm{O}}_4$ phosphor were investigated in connection with its use as a detector of extreme ultraviolet solar radiation in upper atmosphere research. The luminescence of particular interest was a long-period phosphorescence which is excited by wavelengths in the range 1350A to gamma-rays. The energy stored in the phosphor after exposure to short ultraviolet was released by heating and measured by means of a photomultiplier. The stored energy was given by the integrated multiplier response and was independent of the form of the heating cycle. It was also nearly independent of the exposure temperature (-30 to +70°C) and humidity. There was a useful exposure range of ${10}^4$ over which the stored energy was directly proportional to the exposure intensity and time; for higher exposures, saturation set in. The excitation spectrum of the stored energy was measured and the maximum quantum efficiency (5 to 10 percent) was found to lie at 1030A. At room temperature, the long-period phosphorescence decay was of the hyperbolic type. Fluorescence in addition to phosphorescence was excited by wavelengths shorter than 1350A, and an additional excitation band of fluorescence only was found in the region 1400-1600A. The emission spectrum extended from 4480 to 5790A.